London (CNN) -- British police have arrested a couple on suspicion of holding three women captive for more than 30 years, Scotland Yard announced Thursday.
Officers from the Human Trafficking Unit arrested the man and woman, both 67, at their south London home as part of an investigation into slavery and domestic servitude, the Metropolitan Police said. They are in custody.
The "highly traumatized" victims -- a 69-year-old Malaysian woman, 57-year-old Irish woman and 30-year-old Briton -- have been taken to a place of safety, the Metropolitan Police said in a statement.
Police said they'd been alerted in October to the situation by Freedom Charity, which got a phone call from a woman saying "she had been held against her will in a house in London for more than 30 years."
"We applaud the actions of Freedom Charity and are working in partnership to support these victims who appear to have been held for over 30 years.
"We have launched an extensive investigation to establish the facts surrounding these very serious allegations," Detective Inspector Kevin Hyland said.
"We've established that all three women were held in this situation for at least 30 years. They did have some controlled freedom," he told media outside Scotland Yard.
"We've seen some cases where people have been held for up to 10 years, but we've never seen anything of this magnitude before."
Hyland said the women were in "the care of a charity who deal with people who are highly traumatized."
A television documentary on forced marriages relating to the work of Freedom Charity was the catalyst that prompted one of the victims to call for help and led to their rescue.
UK Special Envoy for Human Trafficking, Anthony Steen, told CNN he was unsurprised by the case as there were likely to be many cases of domestic slavery in the country.
"We don't know the number but we know it's pretty huge. Domestics are hidden away," he said.
"The difference between slavery when it was manifest in America -- as it was in England -- was that you could see it everywhere," Steen said. "Since then having abolished it, it's grown, it's got bigger and bigger -- in fact they say it's between 10 and 20 times the size it was in the 1800s."
Steen said the largest number of people involved in slavery in Britain were in brothels and that group was followed by men held against their will in debt bondage.